Replace JSON.load with JSON.parse, also removed the proc parameter

Since we are dealing with untrusted user input, we should not be
using JSON.load. According to the docs[1]:

BEWARE: This method is meant to serialise data from trusted user
input, like from your own database server or clients under your
control, it could be dangerous to allow untrusted users to pass
JSON sources into it. The default options for the parser can be
changed via the ::load_default_options method.

[1] http://www.ruby-doc.org/stdlib-2.0/libdoc/json/rdoc/JSON.html#method-i-load

activesupport/lib/active_support/json/decoding.rb

@@ -13,8 +13,8 @@ class << self
       #
       #   ActiveSupport::JSON.decode("{\"team\":\"rails\",\"players\":\"36\"}")
       #   => {"team" => "rails", "players" => "36"}
-      def decode(json, proc = nil, options = {})
-        data = ::JSON.load(json, proc, options)
+      def decode(json, options = {})
+        data = ::JSON.parse(json, options.merge(create_additions: false))
         if ActiveSupport.parse_json_times
           convert_dates_from(data)
         else

activesupport/test/json/decoding_test.rb

@@ -4,6 +4,12 @@
 require 'active_support/time'
 
 class TestJSONDecoding < ActiveSupport::TestCase
+  class Foo
+    def self.json_create(object)
+      "Foo"
+    end
+  end
+
   TESTS = {
     %q({"returnTo":{"\/categories":"\/"}})        => {"returnTo" => {"/categories" => "/"}},
     %q({"return\\"To\\":":{"\/categories":"\/"}}) => {"return\"To\":" => {"/categories" => "/"}},
@@ -52,7 +58,8 @@ class TestJSONDecoding < ActiveSupport::TestCase
     # tests escaping of "\n" char with Yaml backend
     %q({"a":"\n"})  => {"a"=>"\n"},
     %q({"a":"\u000a"}) => {"a"=>"\n"},
-    %q({"a":"Line1\u000aLine2"}) => {"a"=>"Line1\nLine2"}
+    %q({"a":"Line1\u000aLine2"}) => {"a"=>"Line1\nLine2"},
+    %q({"json_class":"TestJSONDecoding::Foo"}) => {"json_class"=>"TestJSONDecoding::Foo"}
   }
 
   TESTS.each_with_index do |(json, expected), index|
@@ -78,5 +85,11 @@ class TestJSONDecoding < ActiveSupport::TestCase
   def test_failed_json_decoding
     assert_raise(ActiveSupport::JSON.parse_error) { ActiveSupport::JSON.decode(%({: 1})) }
   end
+
+  def test_cannot_force_json_unmarshalling
+    encodeded = %q({"json_class":"TestJSONDecoding::Foo"})
+    decodeded = {"json_class"=>"TestJSONDecoding::Foo"}
+    assert_equal decodeded, ActiveSupport::JSON.decode(encodeded, create_additions: true)
+  end
 end